'unallowably' originates from the English word 'unallowable,' where 'un-' is a prefix meaning 'not,' and 'allowable' means 'permitted.'

'unallowable' changed from the Old French word 'alouer,' which meant 'to allow,' and eventually became the modern English word 'allowable.'

Initially, it meant 'not permitted,' and this meaning has largely remained the same in modern usage.